Mineral composition of Devonian and Quarternary clays of Latvia and its changes on treatment with sulfuric acid solutions

Mineral composition of the Latvian polymineral clays and its changes on the treatment with 5, 10, 15, 20 and 25 % sulfuric acid solutions have been investigated. Devonian (Kuprava and Liepa deposits) and Quaternary (Laza and Ugale deposits) clays were the objects of the present study. The main clayey minerals of the Devonian and Quarternary clays occur to be dioctahedral and trioctahedral illites and kaolinite. All the studied clays contain quartz, dolomite, feldspar, calcite. The following changes occur with the clayey minerals on treatment with sulfuric acid. First, the octahedral network of trioctahedral hydromicas is destroyed. After the partial destruction of the octahedral network sulfuric acid interacts with the sites of the tetrahedral network in which silicon atoms are isomorphically substituted for aluminium atoms. In the course of destruction of the tetrahedral network the simultaneous and proportional substitution of aluminium as well as potassium ions takes place. This confirms the destruction of the trioctahedral hydromicas under the action of sulfuric acid. The intense destruction of the trioctahedral hydromicas under the action of sulfuric acid. The intense destruction of the trioctahedral hydromicas take place both in Devonian and Quaternary clays. Fine-grained kaolinite possessing relatively large number of the sites of isomorphous substitution is strongly destroyed under the action of sulfuric acid, nevertheless kaolinite being present in the Devonian clays. The so-called brucite layer is destroyed in chlorites. Dolomite and calcite present in Devonian and Quaternary clays react with sulfuric acid and are destroyed. Titanium and sodium oxides of the Quaternary clays are included in the clayey minerals not destroyed by sulfuric acid. (author)